Architectural Elements and Depositional Model of Bahamian-Type Ooid Marine Sand Belts Postulated from Surface Features

C. Robertson Handford

Modern marine ooids are currently forming along the platform margins of Great Bahama and Little Bahama Bank as strike-oriented marine sand belts. Other workers showed that these types of sand bodies consist of flood ramps and shields, and cross-cutting channels that terminate in spillover lobes. Sediment transport is generally perpendicular to the sand belt's axis. Although ooid sands are transported locally by daily tidal currents and waves, wholesale movement of an entire sand body probably only occurs during hurricanes.

A completely preserved Bahamian-type marine sand belt should consist of an elongate (parallel with paleostrike), convex-upward body several miles long, and up to about 15-20 ft thick. Isochores should delineate the ramp and shield areas as the thickest zones and the channels as cross-cutting thin zones. Thin channel fills should terminate near leeward margins and pass into thicker zones representing spillover lobes. Large-scale, unidirectional cross-beds should be present in both the basal part of the sand body and in the spillover lobes, and abruptly overlie bioturbated wackestones and/or mudstones of the platform interior. Smaller bidirectional sets should prevail in the upper parts of the sand body. If the sand body prograded during deposition, its seaward margin may contain a grad tional coarsening-upward sequence.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.